--- a/layout/reftests/flexbox/reftest.list
+++ b/layout/reftests/flexbox/reftest.list
@@ -105,17 +105,17 @@ fails == flexbox-inlinecontent-horiz-1b.
 == flexbox-intrinsic-sizing-horiz-1b.xhtml flexbox-intrinsic-sizing-horiz-1-ref.xhtml
 == flexbox-intrinsic-sizing-horiz-2a.xhtml flexbox-intrinsic-sizing-horiz-2-ref.xhtml
 == flexbox-intrinsic-sizing-horiz-2b.xhtml flexbox-intrinsic-sizing-horiz-2-ref.xhtml
 
 # Tests for invalidation after dynamic modifications
 == flexbox-invalidation-1.html flexbox-invalidation-1-ref.html
 
 # Tests for flexbox in an iframe that gets resized.
-fuzzy-if(skiaContent,1,5) == flexbox-resizeviewport-1.xhtml flexbox-resizeviewport-1-ref.xhtml
+fuzzy-if(/^Windows\x20NT\x2010\.0/.test(http.oscpu),1,16) fuzzy-if(skiaContent,1,5) == flexbox-resizeviewport-1.xhtml flexbox-resizeviewport-1-ref.xhtml
 fuzzy-if(skiaContent,1,5) == flexbox-resizeviewport-2.xhtml flexbox-resizeviewport-2-ref.xhtml
 
 # Tests for flexbox styling on things that don't support it
 == flexbox-styling-on-svg-1.svg flexbox-styling-on-svg-1-ref.svg
 
 # Tests with widgets as flex items
 fuzzy-if(gtkWidget,1,66) == flexbox-widget-flex-items-1.html flexbox-widget-flex-items-1-ref.html
 fuzzy-if(gtkWidget,1,74) == flexbox-widget-flex-items-2.html flexbox-widget-flex-items-2-ref.html